JPH08247783A - Transducer - Google Patents

Abstract

PURPOSE: To provide a transducer which includes a simple linearity correcting circuit for simply correcting the linearity error with a mechanical quantity sensor to an extent that no problem substantially arises. CONSTITUTION: The transducer comprises a mechanical quantity sensor 10, and a linearity correcting circuit for analogously calculating its output to obtain a measurement output. The correcting circuit devides the input or output voltage into a plurality of ranges, and switches the input and output transfer characteristics for each range thereby to correct the linearity of the sensor 10 in a polygonal line graph state. The correcting circuit has a plurality of operational amplifiers, and has a level shifting circuit 11 for stepwisely varying the amount of shift of the input voltage before and after the switching point of the range, and an adder or substructure circuit 12 for adding or subtracting the output voltage of the circuit 11 to or from the input voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer for detecting a mechanical quantity such as pressure or acceleration with a sensor and outputting a measurement signal to an application system such as a microcomputer, and more particularly to a linearity error (non-linearity) of the sensor. Linearity correction technique for correcting the linearity between the mechanical quantity input and the measurement output.

[0002]

2. Description of the Related Art FIG. 12A shows an example of a capacitance type acceleration sensor. As shown in the figure, the silicon substrate 1 is processed using a semiconductor process, and the thin beam portion 2 is formed.
A weight 3 is formed in a cantilevered manner via. The silicon substrate 1 is bonded to the glass substrate 4. The movable electrode 5 is formed on the lower surface of the weight 3, and the working electrode 5
The fixed electrode 6 is formed on the surface of the glass substrate 4 facing the. Since both electrodes 5 and 6 face each other with a minute gap, a capacitor is formed between them.

In such a structure, when the weight 3 receives an acceleration in the vertical direction in the figure, the beam 2 is displaced due to bending, and the distance between the electrodes 5 and 6 changes in proportion to the acceleration. Since the capacitance of the capacitor changes with this change, the acceleration can be detected by detecting the amount of change. By the way, since the capacitance is inversely proportional to the distance between the electrodes 5 and 6,
The acceleration input and the sensor output (capacitance) form a curve having an almost inversely proportional characteristic, as shown in FIG.

In the case of the sensor characteristic as shown in FIG. 1B, it cannot be regarded as a substantially straight line if the measurement range is limited to a very narrow range, but in order to widen the measurement range, a straight line is obtained by some method. It is necessary to correct the sex. As is well known, many mechanical quantity sensors have a curve-like characteristic as illustrated in FIG. 1B, and therefore, a measurement circuit portion that drives the sensor and outputs its output, or a sensor output by a microcomputer. The linearity correction processing is performed in the interface circuit portion for inputting into, or the linearity correction is performed by software by digital processing of the microcomputer.

[0005]

In the conventional linearity correction processing, the linearity error (non-linearity) of the sensor is attempted to be smoothly linearized over the entire measurement range. Therefore, either the analog circuit system or the digital circuit system is used. , Very cumbersome to process. By designing an analog function generator that matches the sensor characteristics, it is possible to realize highly accurate linearity over a wide range. However, since such a function generator is a complicated, large-scale, and expensive device, it is not possible to inexpensively realize a transducer in which a sensor drive circuit including a linearity correction circuit and a preprocessing circuit are integrated with a sensor. Have difficulty.

Further, even if linearity correction is performed by software using a processor such as a microcomputer or DSP, the processing scale becomes large in order to realize high-precision characteristics in a wide band,
Therefore, there is a problem in that the linearity correction process accompanying the reading of the measurement data takes too much time and the overhead becomes significantly large. In addition, there is a problem that the amount of memory used becomes too large in the correction by the table lookup method.

The present invention has been made in view of the above background, and an object of the present invention is to solve the above problems and to perform a simple correction of linearity with a mechanical quantity sensor to the extent that there is almost no problem. An object is to provide a transducer including a linearity correction circuit.

[0008]

In order to achieve the above-mentioned object, a transducer according to the present invention comprises a mechanical quantity sensor and a linearity correction circuit that obtains a measurement output by analogically processing the output of the mechanical quantity sensor. The linearity correction circuit is configured to divide the input voltage or the output voltage into a plurality of ranges and switch the input / output transfer characteristics for each range to correct the linearity of the mechanical quantity sensor in a line graph form. Has been done. Here, the linearity correction circuit is configured by using a plurality of operational amplifiers, a level shift circuit in which a shift amount with respect to an input voltage changes stepwise before and after the range switching point, and an output voltage of the level shift circuit. And an adder / subtractor circuit for adding / subtracting the input voltage.

The transducer of the second invention comprises a mechanical quantity sensor, an oscillator whose frequency changes according to its output, a counter which counts the number of output pulses of this oscillator per fixed time, and a count value of this counter. And a linearity correction circuit that obtains a measurement output by digital processing, wherein the linearity correction circuit divides the count value into a plurality of ranges, and switches the addition / subtraction algorithm for the count value for each range. Is configured to correct the linearity of the mechanical quantity sensor in the form of a line graph.

[0010]

In any of the inventions, the linearity error of the sensor is not linearly smoothed over the entire measurement range, but the measurement range is divided into a plurality of ranges and the input / output transfer characteristics are switched for each range. The characteristic of a line graph is obtained by and the characteristic of the mechanical quantity sensor is simply corrected.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the transducer according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows the circuit configuration of the first embodiment of the present invention. As shown in the figure, an input Vin (sensor output) given from the mechanical quantity sensor 10 is processed by a linearity correction circuit configured as follows, and an output is generated.

Here, as the mechanical quantity sensor 10, as shown in the above-mentioned conventional example, not only the capacitance type acceleration sensor but also the capacitance type pressure sensor and the piezo type pressure sensor, It can be applied to all sensors that output analog voltage signals for given mechanical quantities.
The mechanical quantity includes time, temperature, humidity, voltage, acceleration acting on the sensor, pressure, light quantity, and the like. Further, the direct output signal of the sensor itself can take various forms such as voltage, pulse, capacitance, resistance, etc., but is finally output as an analog voltage (capacitance type In the case of an acceleration (pressure) sensor, the voltage corresponding to the capacitance change is output).

The input voltage Vin is input to the level shift circuit 11 and also to the addition / subtraction circuit 12. The level shift circuit 11 receives the input voltage Vin and the constant voltage source 1
3 is compared with the reference voltage Vp from 3 and the output voltage of the level shift circuit 11 is maintained at zero volt when Vin <Vp, and a differential voltage (Vin−Vp) is output when Vin ≧ Vp. ing. Specifically, the constant voltage source 1
It is composed of two and four resistors R1 to R4, and a general-purpose single power supply operational amplifier OP1 capable of outputting up to a negative power supply voltage. The output of the constant voltage power supply 12 is the operational amplifier OP1.
Is input to the inverting input side (subtraction side) of the signal, and the signal Vin from the sensor is input to the non-inverting input side of the operational amplifier OP1. Further, the non-inverting input side of the resistor R3 is connected to GND.
Connect to (0V).

Thus, when Vin becomes equal to the constant voltage Vp, the output becomes equal to GND (0V), and the circuit including the operational amplifier OP1 becomes a subtraction circuit for Vin and Vp.
On the other hand, when Vin becomes lower than Vp, the output becomes OV or less (Vin
Although -Vp <0) is output, if the negative power source of the operational amplifier is connected to GND (0V), this operational amplifier cannot output 0V or less. Therefore, this circuit constitutes a circuit that outputs 0 V when the input signal Vin is smaller than Vp and outputs the difference between Vin and Vp when Vin becomes Vp or more.

The output of the level shift circuit 11 is appropriately amplified or attenuated by the amplification / attenuation circuit 14, and its output is input to the addition / subtraction circuit 12 and added / subtracted with the input voltage Vin from the mechanical quantity sensor 10. The output of the adder / subtractor circuit 12 is provided to the microcomputer as the output of the transducer. The gain of the adder / subtractor circuit 12 is variable resistor R8.
Can be adjusted appropriately.

As is clear from the above description of the structure, the output characteristic of this transducer is as shown by the solid line in FIG. In other words, the point at which Vin = Vp is the range switching point, the measurement range is divided into two ranges before and after that, and the input / output transfer characteristics of the linearity correction circuit are Vin <Vp and Vin.
The range can be switched between ≧ Vp.

More specifically, when Vin <Vp, the output of the level shift circuit 11 becomes 0, so that the output of the amplification / attenuation circuit 14 also becomes 0. Eventually, the input Vin given from the sensor 10 is added / subtracted as it is. It is output from the circuit 12.
Then, when Vin ≧ Vp, an output corresponding to the input voltage Vin is generated from the level shift circuit 11 (shown by a broken line in FIG. 2), and the value is attenuated by the amplification attenuation circuit 14 (one point in FIG. 2). (Indicated by a chain line) in the sensor 1 in the addition / subtraction circuit 12.
By subtracting from a raw characteristic of 0 (input Vin, shown by a chain double-dashed line in FIG. 2), a characteristic like a solid line is obtained.

FIG. 3 shows the circuit configuration of the second embodiment of the present invention. The difference from the embodiment of FIG. 2 is that the adder / subtractor circuit 1
The range is switched based on the output voltage of 2.
That is, the output voltage Vout of the adder / subtractor circuit 12 is input to the level shift circuit 11 and compared with the reference voltage Vp. V
In the first range where out <Vp, the output of the level shift circuit 11 is zero volt, and in the second range where Vout ≧ Vp, the level shift circuit 11 outputs a differential voltage (Vout−Vp).

As a result, the addition / subtraction circuit 12 is used instead of Vin.
Since the level of the output from is determined and the level is shifted, the determination level Vp can be determined regardless of the amplitude level of the sensor signal Vin, and the variation in the sensitivity of the sensor can be ignored.

FIG. 4 shows the circuit configuration of the third embodiment of the present invention. This embodiment is based on the second embodiment described above, and an adder circuit 15 is provided instead of the adder / subtractor circuit 12 in the second embodiment. That is, the inverting adder circuit 16 centered on the operational amplifier OP4 and the inverting amplifier circuit 17 centered on the operational amplifier OP5 constitute the adder circuit 15. The gain of the inverting amplifier circuit 17 is variable resistor R13.
Can be adjusted with.

As a result, even if the output characteristic of the sensor 10 is a signal that is convex upward as shown by the chain double-dashed line in FIG. 5, correction is performed with improved linearity as shown by the solid line in FIG. You can

In all of the above three embodiments, the measurement range is divided into two ranges, but the present invention is not limited to this. For example, as shown in FIG. 6, it is divided into three ranges. The linearity correction can be performed by performing the processing, or the linearity correction can be performed by further dividing into four ranges as shown in FIG. 7. More specifically, in the example shown in FIG. 6, the second and third embodiments (or the first and third embodiments).
A complex signal having an inflection point is corrected by combining (Example). Further, in the example shown in FIG. 7, the linearity is further increased by using a plurality of the first and second embodiments and providing a plurality of level-shifted voltages Vp.

8 and 9 show the circuit configuration of the fourth embodiment of the present invention, and FIG. 10 is a timing chart of its operation. First, as shown in FIG. 8, in this embodiment, the sensor 1
A capacitance type pressure sensor is used as 0, and the difference between the capacitance of the sensor output and the capacitance Cr of the reference unit 20 serving as a reference is taken to cancel temperature characteristics and power supply fluctuations, thereby improving measurement accuracy. . Then, when performing such subtraction, the oscillation circuits 21a and 21b are used to convert to frequencies corresponding to the respective capacities, and the counters 22a and 22b output the number of pulses (count value) corresponding to the frequencies, and the output The subtraction circuit 23 performs subtraction processing on the counted values. Then, when performing the subtraction processing in the subtraction circuit 23, the correction unit 24 for improving the linearity.
A predetermined correction process can be performed based on the correction value data given by And the specific configuration is
As shown in FIG. 9, it will be described in detail below.

First, the role of each oscillator installed on the input side will be described. The first oscillator 21a: the capacitance of the pressure sensor 10 is converted into a frequency. The second oscillator 21b: The capacitance of the reference section 20 is converted into a frequency. 21c: Counters 3 and 4 for linearity correction
The fourth oscillator 21d: A reference clock for determining the operation timing is created.

The first oscillator 21a and the first counter 22a for obtaining the count value C1 corresponding to the output (capacitance) of the sensor unit 10 and the reference unit as shown in the schematic configuration diagram of FIG. It is provided with a second oscillator 21b and a second counter 22b for obtaining a count value C2 according to the output (capacity) of 20. And both counters 2
2a and 22b are configured to input the count values C1 and C2 of the input signals from the oscillators 21a and 21b to the first subtractor 23a that constitutes the subtraction circuit 23 within the constant time E1 set by the timing generator 25. It The first subtractor 23a is for obtaining the raw characteristic before correction based on the measured value, and is configured to obtain the output value S by performing the arithmetic processing of S ← 150 + C2-C1. It should be noted that the reason why 150 is added to the difference between C2 and C1 is that the specifications of the pressure sensor to which the present embodiment is applied set the measurement range to 0 to 600 mmH ₂ O and the output range at that time to 0 to 300 pulses. Since it is set so that C1 =
This is because the center of the output range (150) is set at the time of C2.

The outputs of the first and second oscillators 21a and 21b are the third and third oscillators installed on the input side of the correcting section 24.
Both counters 2 are provided to the fourth counters 24a and 24b.
4a and 24b count the number of pulses input from the oscillators 21a and 21b within a fixed time E2 set by the timing generator 25, and count values C3 and C4 thereof.
Is input to the second subtractor 24c. The fixed time E2 is set to 1/6 of E1 in this example. Note that the adjustment performed so that E2 becomes a desired time changes the oscillating frequency of the third oscillator 21c by changing the variable resistance of the linearity correction unit, and thereby the pulse width E output from the timing generator 25.
This is done by changing 2.

This is because the output of the pressure sensor to which this embodiment is applied has a downwardly convex characteristic as shown in FIG. 11, and the low pressure side (200 mmH ₂ O or less) and the high pressure side (400 mmH ₂ O). The linearity is the best when the correction amount in the above) is a value obtained by subtracting a value that is about 1/6 smaller than the value of the raw characteristic indicated by the chain double-dashed line in the figure. Therefore, in order to obtain the value of ⅙ of the difference data between C1 and C2, the count period is set to ⅙, and the count value of C3 = C1 / 6 C4 = C2 / 6 is extracted, C4-C3 = (C2 / 6)-(C1 / 6) = (C2-C1) / 6 was calculated.

Therefore, in the second subtractor 24c, the calculation process of R ← 25 + C4−C3 is performed to obtain the value R for the pressure corresponding to the characteristic of 1/6 of the raw characteristic S. Then, the R thus obtained is used as the third subtractor 24 for obtaining the correction value on the low voltage side.
It is supplied to the fourth subtracter 24e for obtaining the correction value of d and the high voltage side. Then, in the third subtractor 24d, the calculation process of P ← 17-R is performed to obtain the initial value (temporary value) of the low-voltage side correction value P, and when P is negative, regardless of the above calculation result. Let P = 0. Then, the value P thus determined is given to the first correction value calculation unit 24f.

The first correction value calculator 24f determines whether the output value S of the raw characteristic given from the first subtractor 23a is less than 100 pulses, which is the low voltage side, and the low voltage side is determined. In this case (S <100), the correction value P obtained above is left as it is, and if it is not on the low voltage side, correction on the low voltage side is not necessary, so P = 0. Then, the low-voltage side correction value P thus obtained is given to the fifth subtractor 23b.

On the other hand, in the fourth subtracter 24e, the calculation process of Q ← R-33 is performed to obtain the initial value (temporary value) of the high-voltage side correction value Q, and when Q is negative, the above calculation is performed. Q = 0 regardless of the result. Then, the value Q thus determined is given to the second correction value calculation unit 24g.

On the other hand, in the second correction value calculator 24g,
It is determined whether the output value S of the raw characteristic given from the subtractor 23a is larger than the pulse number 200 on the high voltage side,
When it is determined that the voltage is on the high voltage side (S> 200), the correction value Q obtained above is left as it is, and when it is not on the high voltage side, correction on the high voltage side is not necessary, so Q = 0. Then, the high-voltage side correction value Q thus obtained is used as the fifth subtractor 23b.
Give to. Each of the above counters and subtractor units 24a to 24
g constitutes the correction unit 24. The constants 17 and 33 in the third and fourth subtractors 24d and 24e, respectively, are similar to 25 in the second subtractor 24c and are approximate values of 1/6 of 100 and 200, respectively.

Fifth subtractor 23b constituting subtraction circuit 23
Then, as described above, the first and second correction value calculation units 24f,
The output of 24g and the output of the first subtractor 23a are given,
The correction data of the measured value is obtained by performing the arithmetic processing of T ← SPQ based on these respective values. That is, when the measured pressure is on the low pressure side, the low pressure side correction value P becomes a predetermined value and Q is 0. Therefore, the above equation is equivalent to executing SP, and the correction for subtracting the value of 1/6 of S based on the actual measured value is performed. On the other hand, when the measured pressure is on the high pressure side, the high pressure side correction value Q becomes a predetermined value and P is 0. Therefore, the above equation is equivalent to performing S-Q, and the S of 1 based on the actual measurement value.
A correction of subtracting the value of / 6 will be performed. Furthermore, S is 1
In the central region of 00 to 200, both P and Q are 0, so T = S.

Further, in the present embodiment, the subtractor 23 is provided with the selector 23c, and the selector 23c is provided with the first and fifth selectors.
The subtractors 23a and 23b are input. Then, the selector 23c selects and outputs either the uncorrected data S given by the first subtractor 23a or the corrected data T given by the fifth subtractor 23b by a control signal given from the outside. It is like this.

Then, the output unit 2 outputs a predetermined number of pulses corresponding to the value output from the selector 23c.
It is output from 6. That is, the rising edge of the pulse E3 output from the timing generator 25 causes the fifth counter 27 to start counting the falling edge of the pulse output from the fourth oscillator 21d.

The counter value output of the fifth counter 27 is given to the comparator 28, which compares it with the output (S / T) of the selector 23c, and when the counter value is smaller, The output of comparison 28 becomes L,
The output is switched to H when both match or the counter value becomes larger. And
The output Comp of the comparator 28 and the E3 are output from the output unit 2.
6 is given as a control signal to the output terminal 6, and when this Comp is L and E3 is H, the output unit 26 receives the input (the fourth oscillator 2).
The pulse given from 1d) is output as it is, and it is cut off at other times.

As a result, as shown in the timing chart of FIG. 10, with the rise of E3, E3 = H,
Since the state is Comp = L, the pulse of the fourth oscillator 21d is output as the output pulse OUT. When the count value C5 of the fifth counter 27 becomes equal to S or T, Comp becomes H, so that the output unit 26 is cut off and the pulse output is stopped. As a result, the pulse is output only for the time corresponding to T and S.

The E3, Comp is also given to the reference clock control unit 29. Since the reference clock control unit 29 is composed of a NAND circuit, the Cook
Is switched to H, the reference clock control unit 29
Output becomes L, and the fourth oscillator 21d also stops. After that, each of the counters 22a, 22b, 24a, 24
In addition to resetting b and 27, the timing generator 25 is also reset to prepare for the next measurement.

In the above embodiment, E2 is 1 / E1
However, the constants (25, 17, 33) in the second to fourth subtractors 24c to 24e are not always accurate 1 /
Since it does not necessarily become 6, the variable resistance of the linearity correction unit may be adjusted using this as a guide to further improve the linearity, or the predetermined constant itself may be changed to 1/6. It is not limited to. Furthermore, if the characteristics of the mounted sensor are different, E2 / E1
It goes without saying that the constants in the second to fourth subtractors 24c to 24e are changed.

[0039]

As described above, in the transducer according to the present invention, the linearity error of the sensor is not linearized smoothly over the entire measurement range, but the measurement range is divided into a plurality of ranges, and each range is divided. By switching the input / output transfer characteristics to, a line graph-like characteristic is obtained, and the characteristic of the mechanical quantity sensor is simply corrected. Therefore, the configuration of the correction circuit is extremely simple, and the transducer in which the sensor and the correction circuit are integrally mounted can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of the first embodiment.

FIG. 3 is a circuit configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit configuration diagram showing a third embodiment of the present invention.

FIG. 5 is a characteristic diagram of the third embodiment.

FIG. 6 is a characteristic diagram showing another example.

FIG. 7 is a characteristic diagram showing another example.

FIG. 8 is a schematic configuration diagram showing a fourth embodiment of the present invention.

FIG. 9 is a functional block diagram showing a fourth embodiment of the present invention.

FIG. 10 is an operation timing chart of the fourth embodiment.

FIG. 11 is a characteristic diagram of the fourth embodiment.

FIG. 12 is a diagram showing a configuration and characteristics of an example of a mechanical quantity sensor.

[Explanation of symbols]

 10 Mechanical quantity sensor 11 Level shift circuit 12 Addition / subtraction circuit 14 Amplification attenuation circuit 15 Addition circuit

Claims (3)

[Claims] 1. A mechanical quantity sensor, and a linearity correction circuit that obtains a measurement output by analogically processing the output of the sensor. The linearity correction circuit divides an input voltage or an output voltage into a plurality of ranges. , A transducer characterized in that the linearity of the mechanical quantity sensor is corrected in the form of a line graph by switching the input / output transfer characteristics for each range. 2. The linearity correction circuit is configured by using a plurality of operational amplifiers, and a level shift circuit in which a shift amount with respect to an input voltage changes stepwise before and after the range switching point, and a level shift circuit of the level shift circuit. The transducer according to claim 1, further comprising an adder / subtractor circuit that adds and subtracts an output voltage and the input voltage, or an adder circuit that adds the output voltage of the level shift circuit and the input voltage. 3. A mechanical quantity sensor, an oscillator whose frequency changes according to its output, a counter for counting the number of output pulses of this oscillator per fixed time, and a count value of this counter which is digitally processed to be measured. And a linearity correction circuit that obtains an output, wherein the linearity correction circuit divides the count value into a plurality of ranges, and switches the addition / subtraction algorithm for the count value for each range to obtain a straight line of the mechanical quantity sensor. A transducer that corrects the sex in the form of a line graph.